An example of a conventional reflective member is shown in FIG. 14. The illustrated reflective member 90 is used as a reflective plate for an illuminating device, for example, and includes a metal base 91 having a surface formed with a reflective film 92. The reflective film 92 includes a transparent-resin base material 93 in which particles 94 made of e.g. aero silica gel are dispersed. A difference in refractive index of the base material 93 and the particles 94 is utilized to increase the reflectance (see Patent Document 1, for example).
Since the reflective member 90 utilizes total reflectance due to the difference in refractive index, the reflectance is very high in a band of wavelength where no light is absorbed by the resin material contained in the base material 93. Thus, light efficiency is enhanced in e.g. fluorescent lamp for general lighting. On the other hand, in the reflective member 90, since the base material 93 contains resin, when the base material 93 is irradiated with light in a band of wavelength which is absorbed by the resin, the base material 93 is disadvantageously deteriorated and colored.
The reflective member may be a reflective material “Spectralon” (registered mark) made by compacting resin powder (see Patent Document 2, for example). Such a reflective material has a high workability and is used as a reflectance standard or an integrating sphere. However, since the reflective member also contains resin, when being irradiated with light in a band of wavelength which is absorbed by the resin, the reflective member is disadvantageously deteriorated and colored.
As described above, if a resin is used as a main component of a member for reflection, when the member is irradiated with a light in a band of wavelength which is absorbed by the resin, the resin is deteriorated and colored. As a result, in a reflective member containing a resin, reflectance is disadvantageously reduced due to deterioration of the resin.
Further, in a display device or an illuminating device, heat generated at a lighting circuit further deteriorates and colors the resin, and thus encourages reduction in reflectance. Therefore, it is unfavorable to use a resin for making a reflective member of a device in which a light source frequently emits light, such as a display device and an illuminating device. Especially, in a device using a light source such as an LED and an LD for emitting light of short wavelength (ultraviolet light, near ultraviolet light, or blue light), since the energy of light emitted by the light source is large, deterioration of the reflective member due to light absorption by the resin, or reduction in reflectance, is likely to occur.
The reflective member may also use ceramics made by sintered inorganic particles (see Patent Document 3, for example). Inorganic materials have binding energy generally larger than that of organic materials, and thus have enhanced light resistance and heat resistance. Thus, the reflective member using ceramics is advantageous in that it is less deteriorated due to light absorption, in comparison with the reflective member using a resin which is an organic material.
Patent Document 1: JP-A-11-29745
Patent Document 2: U.S. Pat. No. 4,912,720
Patent Document 3: JP-A-2004-207678